Activity of the dietary antioxidant ergothioneine in a virus gene-based assay for inhibitors of HIV transcription

The "Long Terminal Repeat" (LTR) of HIV-1 is the target of cellular transcription factors such as NF-κB, and serves as the promoter-enhancer for the viral genome when integrated in host DNA. Various LTR-reporter gene constructs have been used for in vitro studies of activators or inhibitors of HIV-1 transcription, e.g., to show that antioxidants such as lipoic acid and selenium inhibit NF-κB-dependent HIV-1 LTR activation. One such construct is the pHIVlacZ plasmid, with the HIV-1 LTR driving expression of the lacZ gene (encoding β-galactosidase, β-gal). Typically, for inhibitor screening, cells transfected with pHIVlacZ are activated using tumor necrosis factor-α (TNF-α), and the colorimetric o-nitrophenol assay is used to assess changes in β-gal activity. A variant of this assay was developed as described here, in which LTR activation was induced by pro-fs, a novel HIV-1 gene product encoded via a -1 frameshift from the protease gene. Cotransfection of cells with pHIVlacZ along with a pro-fs construct produced a signifcant increase in β-gal activity over controls. L-ergothioneine dose dependently inhibited both TNF-α-mediated and pro-fs-mediated increases in β-gal activity, with an IC₅₀ of about 6 mM. Thus antioxidant strategy involving ergothioneine derived from food plants might be of benefit in chronic immunodeficiency diseases.